Yerkes Observatory ( YUR-keez) is an astronomical observatory located in Williams Bay, Wisconsin, United States. The observatory was operated by the University of Chicago Department of Astronomy and Astrophysics from its founding in 1897 to 2018. Ownership was transferred to the non-profit Yerkes Future Foundation (YFF) in May 2020, which began restoration and renovation of the historic building and grounds. Re-opening for public tours and programming began May 27, 2022.The observatory, often called "the birthplace of modern astrophysics," was founded in 1892 by astronomer George Ellery Hale and financed by businessman Charles T. Yerkes. It represented a shift in the thinking about observatories, from their being mere housing for telescopes and observers, to the early-20th-century concept of observation equipment integrated with laboratory space for physics and chemistry analysis.
The observatory's main dome houses a 40 in-diameter (102 cm) doublet lens refracting telescope, the largest refractor ever successfully used for astronomy. Two smaller domes house 40-inch (102 cm) and 24-inch (61 cm) reflecting telescopes. There are several smaller telescopes – some permanently mounted – that are primarily used for educational purposes. The observatory also holds a collection of over 170,000 photographic plates.The Yerkes 40-inch was the largest refracting-type telescope in the world when it was dedicated in 1897, although there had been several larger reflecting telescopes. During this time, there were many questions about the merits of the various materials used to construct and design telescopes. Another large telescope of this period was the Great Melbourne Telescope, which was a reflector. In the United States, the Lick refractor had just a few years earlier come online in 1888 in California with a 91 cm lens.
Prior to its installation, the telescope on its enormous German equatorial mount was shown at the World's Columbian Exhibition in Chicago during the time the observatory was under construction.
The observatory was a center for serious astronomical research for more than 100 years. By the 21st century, however, it had reached the end of its research life. The University of Chicago closed the observatory to the public in October 2018. In November 2019, "an agreement in principle" was announced that the university would transfer Yerkes Observatory to the non-profit Yerkes Future Foundation (YFF). The transfer of ownership took place on May 1, 2020.
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